Description: Foraminiferal evidence from the eastern equatorial Pacific and from the North Atlantic indicates that the dissolution of deep-sea carbonates was intensified during interglacials rather than during glacials, in contrast to widespread opinion. Pleistoccne dissolution cycles introduce a systematic bias into the Interpretation of calcareous fossil assemblages near and below the lysocline zone.

Description: Planktonic foraminifera were collected from an oceanic front off Baja California, Mexico, during April and May, 1965, in connection with studies of the physical oceanography of the front. Four major water masses were present: Southern Surface Water at approximately 0-50 m, Northern Surface Water, forming a submerged intermediate layer between about 150-50 m, Southern Deep Water below 150 m, and Northern Deep Water deeper than 250 m. Planktonic organisms smaller than 2 mm were concentrated in the surface waters, suggesting that food for foraminifera was most abundant there. Organisms larger than 2 mm, considered a measure of potential predators of foraminifera, were abundant in both surface and intermediate waters. Most foraminiferal concentrations were from 1 to 100 specimens per m :J, with the largest concentrations in Southern Surface Water above the front and in deep water along the front. Lowest concentrations were in intermediate water, except in the frontal mixing zone, and at depths below 450 m. Empty shell concentrations were about one-tenth of associated living concentrations. Possible errors of concentration estimates were assessed by comparing paired net and paired tow results. Seventy percent of these estimates appear to be precise within a factor of 1.3. The error introduced by patchiness probably is much larger. Four foraminiferal assemblages are recognized: ( 1 ) Southern Surface Water assemblage, (2) widespread species with southern affinity which apparently tolerate the intermediate water, ( 3) species brought in with the submerged northern water, and ( 4) the assemblage inhabiting the deep waters. The estimated average minimum flux of empty shells was approximately 6% of the living standing crop I day by volume. The relative empty shell output was greater than this for many intermediate water species, and less for species restricted to southern and to deep water. The intermediate layer contributed approximately one-half of the empty shell flux, where specimens with small terminal chambers (kummerforms) were abundant. The sediment produced in the front contained about 50% kummerforms, but the total standing crop of living foraminifera contained only about 10%. The tongue of advected intermediate water may have represented an unfavorable habitat for foraminifera, where northern species were submerged and possibly deprived of food or otherwise impeded in their normal growth. Southern species also may have been displaced from their normal habitat by mixing processes. These displacements are suggested as one cause for the formation of small terminal chambers in specimens inhabiting intermediate depths. Empty shells apparently arise through reproduction, stress from displacement, and predation, with predation being the least important mechanism.